Undercarriages are known that comprise a strut having a slide rod mounted to slide telescopically therein. The bottom end of the slide rod carries an axle or a bogey for receiving one or more wheels. Suspension means are formed between the strut and the slide rod in order to absorb impacts during landing and in order to suspend the aircraft while it is taxiing.
In general, the rod is connected to the strut by a scissors linkage having branches that allow the rod to be pushed freely into the strut while preventing the slide rod from turning in the strut. For undercarriages provided with means for steering the wheels, the scissors linkage is not connected directly to the strut, but rather to a member that is pivotally mounted on the strut (such as an external collar mounted to turn around a bottom portion of the strut, or indeed a tube that is mounted to turn inside the strut). The angular position of the pivotal member is controlled by a hydraulic or electric steering control that acts via the compass linkage to impose an angular position on the slide rod, and thus on the wheels.
It is known that undercarriages are subject to oscillations, referred to as “shimmy”, that result in particular from coupling between bending and twisting modes of the undercarriage. Such oscillations fatigue the undercarriage and can lead to situations that become catastrophic in the event of entering into resonance. Various means are known for damping these oscillations, such as for example providing anti-shimmy check valves in the hydraulic steering controls, or shimmy dampers on the hinge of the scissors linkage.